In a second group of sixteen young people, all of whom are subjects in the open-label phase of the same study, glutamate will be measured (first) in the anterior cingulate cortex at a single point in time when each subject has achieved steady state on the open-label drug riluzole. If the subject tolerates additional time in the scanner, glutamate will also be measured in the left caudate and possibly in the left thalamus. Glutamate levels in this group will be correlated with change in OCD measures.